Wireless communication systems are evolving extensively in order to provide diverse types of communication services, such as audio and video data, and so on. Generally, a mobile communication system corresponds to a multiple access system that shares available system resource (e.g., bandwidth, transmission power, and so on) so as to be capable of supporting communication between multiple users. Examples of the multiple access system include a CDMA (code division multiple access) system, a FDMA (frequency division multiple access) system, a TDMA (time division multiple access) system, an OFDMA (orthogonal frequency division multiple access) system, an SC-FDMA (single carrier frequency division multiple access) system, an MC-FDMA (multi carrier frequency division multiple access) system, and so on. In a wireless communication system, a user equipment may receive information from a base station via downlink (DL), and the user equipment may transmit information to the base station via uplink (UL). The information being transmitted or received by the user equipment may correspond to data and diverse control information. And, diverse physical channels may exist depending upon the type and purpose of the information being transmitted or received by the user equipment.
In a wireless communication system, since a channel between a transmitting end and a receiving end is not fixed, the channel between a transmitting antenna and a receiving antenna is constantly required to be measured. When a pre-arranged signal is exchanged between the transmitting end and the receiving end in order to measure the channel, a decreased amount of amplitude and a phase shift value may be determined, and such information may be transmitted as feedback to the transmitting end. Furthermore, by using this information, non-agreed data information may be reliably detected and decoded. Herein, the pre-arranged signal between the transmitting end and the receiving end may be referred to as a reference signal, a pilot signal, or a sounding reference signal.
As an example of a communication system to which the present invention may be applied, a 3GPP LTE (3rd Generation Partnership Project Long Term Evolution; hereinafter referred to as “LTE”) communication system will now be broadly described.
FIG. 1 illustrates a general view of an E-UMTS network structure as an example of a communication system. Herein, the E-UMTS (Evolved Universal Mobile Telecommunications System) corresponds to a system evolved from the conventional UMTS (Universal Mobile Telecommunications System). The 3GPP is presently carrying out a basic standardization process for the E-UMTS. Generally, the E-UMTS may also be referred to as an LTE system. For details of the technical specifications of the UMTS and the E-UMTS, reference may be made to Release 7 and Release 8 of “3rd Generation Partnership Project; Technical Specification Group Radio Access Network”.
Referring to FIG. 1, the E-UMTS includes a User Equipment (UE) (120), base stations (eNode B; eNB) (110a and 110b), and an Access Gateway (AG), which is located at an end of a network (E-UTRAN) and connected to an external network. The base stations can simultaneously transmit multiple data streams for a broadcast service, a multicast service and/or a unicast service.
One or more cells may exist for one base station. One cell is set to one of bandwidths of 1.25, 2.5, 5, 10, and 20 Mhz to provide a downlink or uplink transport service to several user equipments. Different cells may be set to provide different bandwidths. Also, one base station controls data transmission and reception for a plurality of user equipments. The base station transmits Downlink (DL) scheduling information of downlink data to the corresponding user equipment to notify information related to time and frequency domains to which data will be transmitted, encoding, data size, and HARQ (Hybrid Automatic Repeat and reQuest). Also, the base station transmits Uplink (UL) scheduling information of uplink data to the corresponding user equipment to notify information related to time and frequency domains that can be used by the corresponding user equipment, encoding, data size, and HARQ (Hybrid Automatic Repeat and reQuest). An interface for transmitting user traffic or control traffic can be used between the base stations. A Core Network (CN) may include the AG and a network node or the like for user registration of the UE. The AG manages mobility of a UE on a TA (Tracking Area) unit basis, wherein one TA unit includes a plurality of cells.
The wireless communication technology has been developed up to the LTE based upon WCDMA. However, the demands and expectations of the users and the manufacturers and providers are growing continuously. Also, since other wireless access technologies are constantly being developed, the wireless communication technology is required to newly evolve in order to ensure competiveness in the future. Accordingly, characteristics, such as reduced cost for each bit, extended service availability, usage of a flexible, frequency band, simple structure and open interface, and adequate power consumption of the user equipment are being requested.
Recently, a standardization procedure for a succeeding (or subsequent) technology of the LTE has been under progress by the 3GPP. In the description of the present invention, the above-mentioned technology will be referred to as “LTE-Advanced” or “LTE-A”. The essential difference between the LTE system and the LTE-A system is the system bandwidth. The LTE-A system aims to support a broadband of up to 100 MHz. For this, the LTE-A system encourages the use of a carrier aggregation (or bandwidth aggregation) technology, which achieves a broadband by using multiple component carriers. In order to use a wider (or broader) frequency band, the carrier aggregation (or bandwidth aggregation) uses a plurality of component carriers as a single large logical frequency band. The bandwidth of each frequency block may be defined based upon the bandwidth of a system block used in the LTE system. Each frequency block uses a component carrier in order to be transmitted. Multiple carriers may be used in combination with carrier aggregation and/or bandwidth aggregation.